In the prior art, a motor used in a power window device or the like has a motor body and a speed reducer. The motor body has a yoke housing, wherein a spindle having an armature is rotatably supported. The speed reducer has a gear housing, wherein a worm shaft and a worm wheel are housed. The worm wheel is meshed with the worm shaft. The yoke housing and the gear housing are assembled by moving them in the axial direction. Moreover, the spindle and the worm shaft are coupled on a common axis before the yoke housing and the gear housing come into abutment.
When the spindle of the motor body is rotationally driven, the worm shaft is rotated according to the rotational direction of the spindle. As the worm shaft rotates, the worm wheel rotates at a speed lower than that of the worm shaft but with high torque. Then, the output shaft, coupled to the worm wheel, rotates to transmit its rotating force to an external load.
However, when the yoke housing and the gear housing of the motor are assembled, the mounting area for the spindle and the mounting area for the worm shaft must be aligned (or fitted) while being accurately held on the common axis. This is troublesome and difficult.
On the other hand, the spindle mounting area and the worm shaft mounting area have to be made such that they can be fitted (or connected) in the axial direction when their relative rotational positions are at predetermined positions. As such, they engage in the rotational direction and cannot rotate relative to each other when they are fitted (or connected). For this requirement, the connection portions have a D-shaped fitting bulge and a D-shaped fitting recess. When the yoke housing and the gear housing are assembled, however, the bulge and recess have arbitrary rotational positions. As such, it is also troublesome to position the bulge and recess in the proper rotational direction for their connection (or fitting). As a result, assembly time is increased. The present invention was developed in light of these drawbacks.